arm64: dts: amlogic: odroid-n2: keep SD card regulator always on

When powering off the Odroid N2, the tflash_vdd regulator is
automatically turned off by the kernel. This is a problem
when issuing the "reboot" command while using an SD card.
The boot ROM does not power this regulator back on, blocking
the reboot process at the boot ROM stage, preventing the
SD card from being detected.

Adding the "regulator-always-on" property fixes the problem.

Signed-off-by: Xavier Ruppen <xruppen@gmail.com>
Suggested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Fixes: c35f6dc5 ("arm64: dts: meson: Add minimal support for Odroid-N2")
[khilman: minor subject change: s/meson/amlogic/]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>